The Crew is about 520-620. As for the dueterium, it can be put in the same place as the Gal, and also in the ventral section that the Deflector has now vacated.
The "secondary hull" is more like a "warp hub" with frills
If I extended the so called secondary hull, then the ship will look disproportioned...you compare the saucer length to the sec-hull, and you find that they are very close to each other...the sec-hull would be much more dense as the warp coils are as stated in the TNG tech manual to be rediculously heavy for their size, hence very dense. So, if a toy or miniature of this ship was ever made, the secondary hull would me made in metal, while the saucer would be plastic.